Movies, songs, and other media are often sent to users in an encrypted form. This is usually to protect the media from theft or misuse. But the media still needs to be available for legitimate uses. So some media components are authorized to decrypt and use the media, like some digital video disk (DVD) players or software modules on a computer. These authorized components, when working properly, decrypt media and use it as permitted.
But sometimes an authorized component is found to have an exploit where it can be misused. A person wishing to make an unauthorized copy of a movie, for instance, may find a way to take advantage of such an exploit in a software module that will result in obtaining unauthorized access to the content. When this capability for misuse is learned, the previously authorized component may have its authorization revoked.
Currently, when a component is authorized, it often has a signed certificate proving its authorization. But when the component is compromised, this authorization may be revoked through a revocation list. This list is often sent with each media file so that the receiver of the media file will know whether it should permit particular components to access the media file. This receiver (sometimes called a digital rights management (DRM) device) analyzes the revocation list and determines whether or not to transmit the media file to a component.
But transmitting this revocation list (or lists, as is there are often many of them) can be expensive in terms of network bandwidth. A company that sends a lot of media files, like a cable company or an Internet-based media provider, can spend significant network bandwidth sending revocation lists with media files. Some media providers may even need to transmit the same revocation list for every program they transmit. In addition, sending a proper revocation list with any given content may require infrastructure that some media providers do not yet possess.
This is but one example of a problem with many current protection systems. These systems may also have interoperability problems—such as when a media file cannot be used or properly managed by a receiver that follows a different protection system than the transmitter of the media file.